Okay all you boroscope guys

Silvaire

Silvaire

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Silvaire
41/80 exhaust valve leak. Pulled the cylinder and this is what it looks like looking right down the barrel.

Still think a borescope or a $35 dental camera is gonna tell you somethign you don't already know?

DSCN6017%255B1%255D.JPG
 
Yes, your exhaust valve is f'ing tuliped as hell. Could have caught it way earlier by inspection.
 
What would likely cause that? Overheating the valve from: mixture too lean , RPM too high, timing too advanced...?
 
Agree with stuck valve, I have no idea what "tuliped" means. I think you are just seeing some anomalies caused by the cameras flash. All I see is a slight discoloration of the exhaust valve seat at the lower right. Last annual the cylinder compression was 75/80. Engine ran fine and there were no indications this annual other than low compression.

So if you were able to see that slight discoloration with a videoscope or dental camera and the compression test was good what action would you have taken that would have resulted in a different outcome?

My bet is that at last annual, when compression was good, the slight discoloration wasn't there.
 
Borescopes are very handy tools. Even for looking those parts of your body that are hard to reach, specially if you are obese.
 
What's neat is that car guys say that leaded fuel will prevent that. Unless they install hardened seats. So when you drop off a set of heads for a valve job, and don't allow them to replace the seats, they won't warrenty the heads, unless you run a lead additive in the fuel. :rolleyes:

Tulip valve is caused by too much spring pressure, for the temps.
My guess, is that it's sticky valve caused by leaded fuel, or to tight guide, or both.
 
FORANE said:
What would likely cause that? Overheating the valve from: mixture too lean , RPM too high, timing too advanced...?
Click to expand...
Advanced timing will not cause it. Retarded timing will.
Too far advanced will cause other troubles, hard starts, and kick back for one. Running a perfect mixture could cause it, not too rich, not too lean.
Which is possable on a carbutretted engine to do on only one cylinder.
 
bluerooster said:
Tulip valve is caused by too much spring pressure, for the temps.
Click to expand...

Okay but for the record this valve ain't "tuliped" it's just some sort effect from the flash. If you look in there the face is as flat as the Black Rock Desert (which is flatter than a pancake)
 
Newby question: which is which? Is the biggun Ex or In?
 
jhausch said:
Newby question: which is which? Is the biggun Ex or In?
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Exh is always the smaller one AFaIK. Exhaust gas has a higher differential pressure across the valve so that gas move faster and doesn't need as big a hole. Also the smaller the valve the easier it is to cool.
 
gismo said:
Exh is always the smaller one AFaIK. Exhaust gas has a higher differential pressure across the valve so that gas move faster and doesn't need as big a hole. Also the smaller the valve the easier it is to cool.
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For all aircraft engines I've seen this is true.

The only exceptions I've seen are when you have an odd number of valves per cylinder, like a 3-valve arrangement that you find on some cars and motorcycles. In that case, you'll see two small intake valves and the one larger valve is the exhaust.
 
Silvaire said:
Okay but for the record this valve ain't "tuliped" it's just some sort effect from the flash. If you look in there the face is as flat as the Black Rock Desert (which is flatter than a pancake)
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never said it was "tuliped" (that was someone else) just stated fact.

But from what I can see in the pic, the edges look a tad sharp. But that's in the pic.
I notice the intake valve has what appears to be a small chunk out of it's edge just about left center. probably just camera tricks, or something just as benign. So it's been a day or so.
What'd ya'll determine as to the cause?
 
O-360, 550 hrs SMOH, no idea how many total hours are on the cylinder. I took it to the machinist and a quick test shows both valves leaking, about 50% on exhaust. He also noted what looks to likely be a crack between lower plug and exhaust valve. With the price of individual parts and labor involved it's pretty much impossible to beat $1187 for a brand new Lycoming cylinder which comes with everything including new piston so that's my recommendation.

My point is that, as bad off as this thing is, you wouldn't really know it just to look at it, especially in-situ with a $150 320x280 video-scope. Even the suspected crack, you'd have to blast and dye check to be certain. I'm always hearing people claim that a quick peek with a borescope will tell you all you need to know. I disagree.
 
Silvaire said:
I'm always hearing people claim that a quick peek with a borescope will tell you all you need to know. I disagree.
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That's total BS. You overstate what's been said about the value of borescopes as badly as you overstate their uselessness. Can't you find another drum to beat? I'm guessing you make a lot of money pulling cylinders. Most Busch detractors do. But he manages the maintenance on so many more planes than you do that I'd be ****y about it too.... :redface:
 
gismo said:
Exh is always the smaller one AFaIK. Exhaust gas has a higher differential pressure across the valve so that gas move faster and doesn't need as big a hole. Also the smaller the valve the easier it is to cool.
Click to expand...

And the gas's temperature reduces its viscosity so it flows easier. I think that the much higher speed of sound in hot gases might have something to do with it, too. No shock waves to deal with.

Dan
 
Dan Thomas said:
And the gas's temperature reduces its viscosity so it flows easier. I think that the much higher speed of sound in hot gases might have something to do with it, too. No shock waves to deal with.

Dan
Click to expand...

That and............ Motors are a positive displacement piece of machinery.

1- The heat of the burnt exhaust mixture causes expansion and when the exhaust valve opens before bottom dead center on the compression stroke the waste gas is already under pressure to try and find a way out.

2- Pushing the exhaust gas out using the piston on the exhaust up stroke is ALOT more efficient then using the piston to suck the next intake charge into to cylinder.. On naturally aspirated motors the intake needs to be larger... On turbo / supercharged motors the intake charge is ready to be blown into the cylinder when the intake valve opens, that gives better cylinder fill and more power.... On some of the modified tractor pull motors running three, progressively staged turboes and running over 120 PSI of intake manifold boost pressure I have seen the intake valves on those were actually smaller then the exhaust valves.....

Ps.... For the pilots who are not sure how much boost pressure that is... Imagine the manifold pressure gauge in your plane reading over 250 inches....:eek::hairraise::yikes:
 
Despite reopening a month old thread I do believe you when you say you are not interested. I know this because you obviously have never bothered to read Table 1 in TCM's SB03-3 nor listen to anything anyone other than Mike Busch has to say about it.

Let me simplify it for you - this is what TCM says:

if the compression is below the limits
look inside the cylinder with a borescope
if you don't see anything wrong
fly the airplane for 45 minutes and do another compression test
if the compression is still below the limits
replace the cylinder

The only thing I've ever said about this is that if you look in the cylinder with a borescope or a $35 dental camera and actually see a burnt valve face your compression reading is going to be ZERO
 
The way you can twist things around you should work with Carney at the white house....
 
Silvaire said:
41/80 exhaust valve leak. Pulled the cylinder and this is what it looks like looking right down the barrel.

Still think a borescope or a $35 dental camera is gonna tell you somethign you don't already know?

DSCN6017%255B1%255D.JPG
Click to expand...

I just had a jug pulled based on finding a burned valve with a $55 dental camera. Trying to put the picture up with no luck yet, but it was clearly marked with a line across one edge and had limited time before it would have failed.

I have looked at the picture posted and can't see where that valve is failing. Perhaps it is clear to everyone else, but could you tell me what you are seeing and how that would cause that valve to fail? I understood some even discoloration to be normal. Actually that cylinder looks really clean. I am probably missing something.

One other clear sign of a valve failing is a rhythmic rise and fall on the EGT of the cylinder in question. That was not evident yet in the valve I found.
 
Sailer said:
I have looked at the picture posted and can't see where that valve is failing...
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Which was my original point, the valve was failing yet there are no visible signs that could be detected by borescope inspection. In your case, are you saying the compression test was satisfactory but the valve was visibly damaged?
 
Silvaire said:
Which was my original point, the valve was failing yet there are no visible signs that could be detected by borescope inspection. In your case, are you saying the compression test was satisfactory but the valve was visibly damaged?
Click to expand...

No, when we pulled it in and checked compression on that cylinder was 0. That one was easy. I had one a year ago that was pulled only on compression. Nothing showed in the borescope or when the cylinder was pulled. I wish I had that one back to try staking the valve and re-flying. Bet the compression would have come right back.

So you are saying the problem with the valve in the picture was in the stem (wobbling) or something that can't be seen on the face? If that is the case, I get it now.

But would that not simply be an IRAN of the exhaust valve and seat? That requires a replacement of the entire cylinder? I guess if it has been IRAN'd previously that makes sense. But if it only had 550 hours?

With the crack, when pulling the last cylinder for the burned valve the cylinder shop said it had a crack from the top plug to the fuel injector port. We replaced the cylinder but asked for the old one back. Many people have looked at pictures and no one has been able to point out a real crack. I cleaned it up and still can't find anything. I am having it dye tested again before I chunk it. Will keep you posted.

Be careful out there with false positives for cracks. Demand a high resolution picture of the crack with dye penetrant clearly showing.
 
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Sailer said:
No, when we pulled it in and checked compression on that cylinder was 0.

So you are saying the problem with the valve was in the stem (wobbling) or something that can't be seen on the face? If that is the case, I get it now.
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Getting a 0 on a compression test is VERY hard to do....Unless the entire piston or both valves are missing..:confused:
 
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N801BH said:
Getting a 0 on a compression test is VERY hard to do....Unless the entire piston or both vavles are missing..:confused:
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I did not actually do the test, but was standing there when it was done. It showed 0. I have the valve on my desk. It wobbles on a flat surface. I have to assume that would do it?
 
N801BH said:
Getting a 0 on a compression test is VERY hard to do....Unless the entire piston or both valves are missing..:confused:
Click to expand...

No it isn't, the differential compression tester has a restrictor orifice that will only allow a specific flow rate into the cylinder. A stuck valve will easily overcome that and result in 0/80.

Yes the cylinder can be IRAN'ed but there is a point where new parts and labor cost can barely beat the price of a new cylinder, especially if there are any cracks. Also, 550 hours on an overhauled cylinder doesn't tell you how many total hours have been put on it unless you have records on it all the way back to when it was new. So it depends on these factors how you want to go with it.
 
Silvaire said:
O-360, 550 hrs SMOH, no idea how many total hours are on the cylinder. I took it to the machinist and a quick test shows both valves leaking, about 50% on exhaust. He also noted what looks to likely be a crack between lower plug and exhaust valve. With the price of individual parts and labor involved it's pretty much impossible to beat $1187 for a brand new Lycoming cylinder which comes with everything including new piston so that's my recommendation.

My point is that, as bad off as this thing is, you wouldn't really know it just to look at it, especially in-situ with a $150 320x280 video-scope. Even the suspected crack, you'd have to blast and dye check to be certain. I'm always hearing people claim that a quick peek with a borescope will tell you all you need to know. I disagree.
Click to expand...

We only need ask you and we know all we need to know.
 
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